Antibiotic A-28086 factor D is a newly-discovered member of a group of polyether antibiotics. Examples of members of this group include the earlier-discovered antibiotic A-28086 factors A and B (see copending U.S. Pat. application Ser. No. 477,954, filed on June 10, 1974); monensin (U.S. Pat. No. 3,501,568); dianemycin [R. L. Hamill, M. M. Hoehn, G. E. Pittenger, J. Chamberlin, and M. Gorman, J. Antibiotics 22, 161 (1969)]; nigericin [L. K. Steinrauf, Mary Pinkerton, and J. W. Chamberlin, Biochem. Biophys. Res. Comm. 33, 29 (1968)]; and salinomycin (U.S. Pat. No. 3,857,948).